Elastomeric check valves are used to control fluid flow in a variety of applications. Such check valves are typically mounted either on or in the end of a conduit such as a pipe, and are designed to permit flow through the pipe in one direction only, and to seal shut to prevent back flow in the conduit.
Elastomeric check valves typically have what is commonly referred to in the art as a “duckbill” appearance, having a pair of opposed sidewalls which converge toward one another and terminate in a pair of resilient lips which define a slit opening at the outlet end of the valve. Check valves must be sufficiently rigid to resist collapse, also known as “inversion”, for example when the valve is acted on by a back pressure, yet the lips must be flexible enough to open under relatively low inlet fluid pressures so as to minimize the pressure drop, or headloss, across the valve. Furthermore, the length of the slit opening at the end of the valve must be sufficiently large so as to minimize the headloss.
A number of check valve designs have been proposed in the prior art to deal with these concerns. Some prior art valves have enlarged bills with slit lengths greater than the valve diameter in order to minimize headloss. However, such valves generally cannot be installed inside pipes, and have limited application where ground clearance is limited. Furthermore, valves with enlarged bills are prone to sagging and drooping, resulting in poor closure and leaking. The issue of sagging has been addressed in the prior art by providing curved bills, while inversion has been addressed by providing the valve body with secondary reinforcement which helps the valve to maintain its shape under back pressure. None of the solutions proposed to date have been entirely successful in addressing the issues of headloss and inversion resistance over the range of applications in which check valves are typically used. As a result, there are a relatively large number of valve designs on the market, each of which is suitable for a relatively narrow range of applications.
Therefore, there is an unsatisfied need for a check valve which provides relatively low headloss and high inversion resistance, and which can be used in a wide variety of applications.